


On the Sighs of a Dying Sun

by Lokne



Category: Harry Potter - J. K. Rowling
Genre: Alternate Universe - Soulmates, F/M, Falling In Love, Family Drama, Female Regulus Black, Fluff and Angst, Genderswap, M/M, Soulmate-Identifying Marks, Walburga Black's A+ Parenting
Language: English
Status: Completed
Published: 2020-01-09
Updated: 2020-01-09
Packaged: 2021-02-27 12:28:59
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,450
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/22187119
Author URL: https://archiveofourown.org/users/Lokne/pseuds/Lokne
Summary: “Oh, is this your little sister?” James asked, as he flopped on the seat next to Sirius. He thrust his hand toward her as a bright grin split his face.  “James Potter. Nice ta meet you, Reggie.”
Relationships: James Potter/Female Regulus Black, Regulus Black/James Potter, Sirius Black/Remus Lupin
Comments: 20
Kudos: 913





	On the Sighs of a Dying Sun

**Author's Note:**

> For Zee2772 on tumblr. I hope you enjoy!

**FIRST YEAR**

Regenia Black scowled out the window of the Hogwarts Express. Where was he? Sirius had run ahead to meet his best friend, James Potter. He promised he would find her on the train and sit with her. Sirius knew she was nervous. Regenia never liked to show her emotions. Her entire family took advantage of the smallest weakness.

“Liar,” she muttered.

James Potter. She hated him. He wrote to Sirius all summer. Regenia heard Sirius laughing in his room at odd hours of the day. Sirius’ familiar warm bark of laughter had become rare the last few years. And though she treasured its return, she envied the person who brought it back.

She used to follow him everywhere. Sirius caught her when she fell taking her first steps. Her first word was a butchered version of his name. She trailed after him during lessons and mimicked his motions and the way he spoke. He was her perfect older brother.

Then he received his Hogwarts letter. She had never seen him smile that way before. It took her months after he left to realize it was happiness. 

“There you are, Reggie,” Sirius said, sticking his head through the open compartment. 

He spoke as if she had been missing. 

“What’s wrong?” Sirius demanded, sitting across from her. His gaze was locked on the arms folded across her stomach. 

Regenia shook as a flash of anger flooded her. How dare her body betray her like that. She placed her hands on her lap. She folded her arms only when she was emotionally hurting or unsure of herself. Regenia hated that Sirius knew her well, but not well enough to not comment on her weakness.

The area was too close to the soulmark — a vibrant golden sun — that rested on her left hip. Only her parents knew her soulmark and placement. The soulmark tingled as if it wanted to be touched. She resisted the urge for the reassurance that always followed. Not today. Today she would be strong on her own.

“It’s gonna be okay, Reggie—”

“I’m fine,” Regenia rebuked. She waved the hands on her lap as if the last few moments had been erased. See? She was fine. Nothing was wrong. 

“Look—”

“Hey, Sirius, what’s taking so long?” an unfamiliar boy demanded as he entered the compartment.

James Potter. It had to be. Black messy hair, hazel eyes, and a Potter family crest on his dress robes. Regenia glared at his unwanted intrusion into their conversation and life. 

“Oh, is this your little sister?” James asked, as he flopped on the seat next to Sirius. He thrust his hand toward her as a bright grin split his face. “James Potter. Nice ta meet you, Reggie.”

Regenia waited for Sirius to correct him. Only Sirius was allowed to call her Reggie. When the silence extended into awkwardness, James dropped his hand. She swallowed around the rude words that wanted to spill into the air. She knew Sirius would ignore her for the rest of the trip if she insulted James. He was petty at times. 

“Regenia.”

“What?” James asked.

Regenia snorted and rolled her eyes. She grimaced at the narrowed look Sirius shot her. It was true, then. James was important to him. How important? Regenia needed to find out fast if she wanted to keep hold of her brother’s affections. 

“Only Sirius can call me Reggie,” Regenia stated as if her heart hadn’t fallen into her stomach.

Last year she wanted nothing more than to follow Sirius to Hogwarts. Now she was regretting that wish. 

“Riiight.” James nodded and immediately turned to Sirius. “So, are we going to go find Remus and Peter? They’re near the front. Remus promised to save us a seat.”

Sirius laughed. “How did he manage that?”

James grinned. “It’s a secret.”

Sirius jumped to his feet and then glanced at Regenia. “Uh, you wanna come?”

Regenia shook her head. No. She didn’t want to be in the same place as Sirius’ friends. She wouldn’t be able to handle it. 

James shrugged and grabbed Sirius’ hand. “C’mon, Siri, let’s go. She’s good. She said so herself.”

Siri. The nickname she had given Sirius when she was four. 

Regenia blocked out the rest of their conversation and departure. Her head tumped against the glass. The scenery blurred as tears filled her eyes. Regenia’s arms wrapped around her stomach. Alone. Again. 

She hated James Potter. 

**SECOND YEAR**

“You’re not trying out. I forbid it,” Sirius snarled. He grabbed Regenia’s arm and pulled her away from the other members of Slytherin trying out for the Quidditch team. 

Regenia jerked her arm out of his grip. So he was speaking to her again, was he? He hadn’t spoken to her for most of the summer. He spent more time with James Potter and his _friends_ than he did with his own family. Regenia glared at Sirius’ waiting posse, consisting of James Potter and Remus Lupin. 

Sirius hadn’t even waited until they were alone. He publically humiliated her in front of her house and his friends! He was just like their father. She wondered how fast he would explode if she ever uttered those words aloud.

She knew Sirius hated Grimmauld Place. He avoided home like it was a death curse. Sirius wasn’t at home to protect her any more. He had no right to _protect_ her at school.

“I am. Your opinion doesn’t matter,” Regenia retorted. 

Sirius hated that phrase. It was a favorite of their father. She smirked at his shocked expression. Sirius wasn’t allowed to pick and choose when to care about her.

“I’m going to join the Slytherin Quidditch team and we’re going to win the House Cup,” she bragged. She was the best Seeker Sirius had ever seen. 

“Siri, just let her try out,” James said. He wrapped an arm around Sirius’ shoulders and leaned against his side. 

Regenia scowled as his piercing gaze roamed over her body. She was small and agile. Her ebony hair was pulled back into a sensible ponytail for the tryout. Her new broom was polished and waiting for her command. She would make it. She was the best. Siri — _she_ said so. Regenia took a deep breath and straightened her posture. 

“I’m a better player than you are.” Regenia forced her eyes away from Potter and concentrated on her brother. 

James wasn’t worth her attention. He was probably just saying that to get in her good graces. Regenia fought for Sirius’ attention last year and barely succeeded. She wasn’t going to lower her pride this year. Either Sirius wanted to spend time with her or he didn’t. She wasn’t a Crup begging for her owner’s affection. She was Regenia Black. 

“You are.”

Regenia nodded in confirmation. It was fact. Sirius was mediocre at best and had failed tryouts for the second year in a row. Regenia waited.

“You could get hurt.”

Rolling her eyes at his words, Regenia sighed. “You’re acting like I’ve never broken a bone or fallen off a broom. I’ll be fine.”

Sirius ran a hand through his hair in frustration. “I hate that word. Fine. You always say you’re fine. What if—”

“Sirius, you’re treating her like a toy you don’t want to give up,” Lupin interjected with a weary sigh. “Just let the poor girl play. We still have that essay due tomorrow. You know, the one you _haven’t_ started.” 

“Buuut, Mooney!”

Lupin flushed red and then paled at the appellation. “Homework. Now.”

“Damn. That’s tomorrow?” James demanded. “C’mon, Sirius. She’ll be fine.” 

“Okay. Okay. Geez.” 

Once again, Sirius ignored her and listened to his friends. Regenia shook her head to dispel the depressing thoughts. It didn’t matter.

“Good luck, Reggie,” James called out when they started to walk away.

That arrogant jerk! Regenia threw a tripping jinx at his back and snickered when he tumbled to the ground and pulled her brother with him. 

“I don’t need luck, Potty.”

Regenia brushed across her soulmark and grinned viciously at her pathetic competition. She didn’t need her brother; she had her soulmate to support her.

**THIRD YEAR**

“ _Expecto Patronum_.” 

Regenia sighed as the spell failed again. She’d shut herself in this abandoned classroom two hours ago. Her wand movement was perfect. Her pronunciation was spot on. It was her memories that were lacking. 

“Your memory wasn’t happy enough,” an irritatingly familiar voice said.

Regenia growled in frustration. “Shut up, Potter.” 

She didn’t want him here. Her gaze flickered to him. He was alone. She frowned. Why was he alone? It was rare to see James without Sirius.

“Sirius mentioned you couldn’t get the spell right. He knew you’d kick him out if he tried to help you. He said you might just yell at me instead.” James walked further into the room when Regenia didn’t immediately order him to leave. 

Regenia reluctantly chuckled at his answer. Sirius was right. She would have hexed him the moment he set foot in the room. He was a terrible teacher. He possessed no patience. 

“So he sent you? What could you possibly teach me that I don’t already know?”

“You need a happy memory.”

“I know that!” Regenia snapped back. She wasn’t stupid. She just couldn’t think of one. Every memory she tried involved Sirius, and the pangs of bitterness and envy she felt tainted them. 

“Do you?” James asked. 

He grabbed one of the chairs she had set to the side and spun it around so he could lean his chest against the back of it. His chin rested on his crossed arms placed on top. 

“You seem to be struggling with the easiest part.”

Regenia lowered her wand in shock. Easiest part? James must lead a happy, easy life to be able to utter those words so casually. 

“It isn’t,” she mumbled. Her shoulders slumped as she thought about the last two hours of failure. 

“What?” James asked surprised.

“I can’t think of a happy memory,” she admitted through gritted teeth. 

She hated showing weakness. But according to Sirius, James cast a corporeal Patronus on the first try. Sirius could only produce mist. 

“You must have been happy at some point in your life!” James objected. “Sirius said—”

“Sirius is stupid.”

James threw his head back and laughed. The deep happy sound wormed its way into her ears and left them ringing. The warmth of his laugh lingered in the room once he finally stopped. She had never made him laugh before. He gestured at the empty seat next to him.

Feeling contrary, she chose the seat two spots away from him. She glared at his snicker. That wasn’t supposed to be funny. 

“He is. But he’s stupidly smart, too.” 

Regenia nodded. Sirius was that, too. “So… a happy memory, huh?” 

She took a deep breath and thought about what a happy memory meant to her. Had it been that long? 

“It shouldn’t take that long, Reggie. It’s not that complicated,” James said, breaking the silence. “What makes you smile? What gives you comfort when you have a bad day? What do you count on?”

Regenia asked, “What’s your memory, Potty?” and smirked at his wince. He would stop with the nickname, eventually.

“My soulmate.” 

Her heart picked up speed. The sound thumped loudly in her ears. His soulmate. Of course his favorite memory was about his soulmate, Lily Evans, if the rumors were to be believed. She had forgotten.

Her soulmate would be perfect! He had always been there for her. When she fell off her broom for the first time and broke her leg. The time her parents locked her in her room with no dinner because she yelled at an old witch during a party. When Sirius abandoned her for James. His magic hugged her on the train to Hogwarts. 

“ _Expecto Patronum_.” 

A beautiful silver swan burst from the end of her wand. It flew a circuit around the room before hovering a foot in front of her face. A swan represented the rising glory of a new day and the farewell of the setting sun. Her soulmate would never leave her side. 

Regenia leaped from her chair. “I did it!” 

She beamed at James without thought. Her smile dimmed at his answering grin. She didn’t like him! His hazel eyes twinkled too much and his grin was too charming. 

“See. Not hard at all.”

“Shut up.”

**FOURTH YEAR**

“Stop ignoring me, Reggie,” James stage-whispered across the table in the library. “It’s rude.”

Regenia scoffed. He had waltzed into the library thirty minutes ago, noticed her studying, and decided to annoy her. There were seven other tables available.

“You’re rude!” 

A pall of silence filled the space around them. She glanced up when he remained quiet. His painful expression was one she had never seen before.

“I am, aren’t I? I’m rude and cruel. I don’t think before I act. I should have known better, Reggie.”

She glanced away from the vulnerability she saw. It made her uncomfortable. 

“You’re not rude all the time,” she admitted.

A bitter chuckle followed her statement. “Right. Only most of the time. I know. I-I just really thought it was her.”

Ah. Lily Evans. 

Regenia knew the Marauders, as they had taken to calling themselves this year, had pissed off Lily Evans and Severus Snape. For the last two years, James had followed Lily Evans around as if she was the answer to every question. Regenia had assumed, like everyone else, that Lily was James’ soulmate. 

When Lily continued to reject James’ requests for dates and returned his presents, he became desperate. 

With no other option, according to rumors and speculation, James cursed Severus to hang upside down as a way to blackmail Lily into a date and open her eyes. Clearly, James was a better choice than Severus. Lily ordered James to release her soulmate, cut James to the quick with a few spoken words, and stormed off. 

The incident spread through the entire school in a matter of minutes.

James made an error in judgement. Regenia couldn’t fault him. She knew she had a dark streak. Every Black had a small nugget of madness and cruelty in their magic. She couldn’t count the number of times she wanted to cast forbidden dark magic at James during her first year. He would have ended up in the hospital wing if she had retaliated like she had longed to do. 

She still didn’t like James. 

She wished she could list every characteristic that was evil and wrong. She couldn’t. 

He wasn’t a bad person; he made bad decisions. 

“You can hide here,” Regenia said not glancing up from her essay that was due in two days. 

She knew the whispers and judgmental rumors that hadn’t let up for the past week. His hazel eyes were dimmed with shadows and he had dark circles under his eyes. He clearly wasn’t sleeping well. 

“Thanks, Reggie,” James whispered as he piled his arms on the table and placed his head on them.

“I didn’t say you could continue to annoy me. Go to sleep.” 

**FIFTH YEAR**

“Regenia, wait! Please!” James begged as he ran after her.

Regenia ignored his pleas and continued to stride toward the Slytherin common room. “No, Potter. You-you don’t get to say that! Not now.”

James grabbed her arm when he finally caught up to her and he gently pulled her to a stop. “I’m sorry. When I offered Sirius sanctuary, I never thought he would be forced to accept.”

“Forced?” Regenia demanded. “He wasn’t forced. He left. Father—” 

She gasped and took a shallow breath. She had to get her breathing under control. Why did James always see her when she was emotional? 

“He left, Potter.”

James frowned at her response. “He had no choice. Your father is … _unreasonable._ He gave Sirius an impossible choice, Reggie. What was Sirius supposed to do?”

Regenia’s fingers clenched and unclenched in her robes. She knew her mother and father had high expectations for Sirius. They treated him like a pawn more than a son. They had ever since he’d been Sorted. As if being Gryffindor warped him. 

She knew that. She understood why he left. She did. But did he have to leave her behind? Was she so unloveable? Would her soulmate even love her? Every time she thought Sirius wanted her, he cast her aside for someone else. She was tired of picking up the pieces of her heart.

“You stole Sirius! You…” She swallowed the rest of the accusation that wanted to spill into the air. James stole her brother. He took the one person that loved her. 

“It’s his soulmate, Reggie,” James said, deep emotion spilling into every word.

So, he finally found them. 

In the end it hadn’t even been James that ripped her brother from her grasp. It was the one person that could give Sirius everything he needed and wanted. She had spent so many years feeling annoyed and betrayed by James Potter that she had never considered Sirius’ soulmate. 

She wanted to be happy for him. Her heart held too much hurt. She mustered a smile regardless. 

“That’s great, Potter.”

“No. Don’t do this.” James grabbed her shoulders and shook her. “Don’t you dare shut me out, Reggie. You can’t. He needs you.”

Regenia shook her head rapidly. No. He didn’t. She had tried, so many times. She stepped away from James.

“Who?”

“Lupin. They both have a moon soulmark.”

Moon. Sirius had a moon soulmark. She had a sun. Different sides of the same coin. “Fitting.”

James searched her face with intense eyes. He opened his mouth, closed it, and then spoke. “I suppose…” 

He reached out a tentative hand toward her. 

“I’m sorry, Reggie.”

Regenia laughed wetly. “Don’t be. I’ll be fine.” 

She turned away from James. After a few feet she glanced over her shoulder and uttered the words she never thought would cross her lips. 

“Take care of him for me. He’s stupid.”

“He’s stupidly smart, too,” James said, completing the ritual that had formed during her third year. They said it every time they talked about Sirius.

A reluctant chuckle escaped her. She bit her lip as sobs worked their way out of her chest. Sirius wasn’t her brother any more. Sirius Black was considered dead by the entire Black family. She curled into herself. 

Strong arms wrapped around her from behind. She spun around and latched onto James with all the power she had remaining. 

Damn James Potter. 

If Sirius had never met him, he never would have found Remus Lupin. 

James was too kind. His arms were too warm and comforting. 

**SIXTH YEAR**

Walburga and Orion wanted to present her to the Dark Lord. Regenia couldn’t bear to call them her parents. The moment she read the damning letter the family owl had dropped in front of her at breakfast had ended the tenuous relationship. 

She resented them for excommunicating Sirius from the family, but— 

Regenia never thought they would pawn their only remaining child onto the Dark Lord. 

She felt stupid. 

When Sirius had left home for good, Walburga started grooming her. The once weekly lessons changed into daily. The books she was required to read delved into darker and darker arts. The spells became more malicious and cutting. Regenia had truly been bathed in the Black family magic during the summer. 

She was still trying to cast off the feeling.

Pacing the Room of Requirement, she shuddered at the thought of belonging to the Dark Lord. If she received the Dark Mark, it would override her soulmark. The twisted magic of the Dark Mark would sever the soulbond and bind her soul to the Dark Lord. 

She placed a hand on the sun on her left hip. The color had faded the last few weeks. Her connection to her soulmate was in perilous danger and there was nothing she could do about it.

“I wish James were here. He’d know what to do,” Regenia muttered. 

“You Summoned me?” James asked. He folded up a blank piece of parchment and placed it in his robe pocket.

“How did you know?” Regenia rubbed her forehead. 

How did he always know where she was? There had to be something special about that parchment. It wasn’t the first time she had seen it.

“My hip hurt.”

“What?” she asked with confusion.

Regenia stopped pacing. What did that have to do with anything?

James quirked a sad smile. “You still don’t know? After all these years?” 

He growled and ran a hand over his face, pushing his glasses askew. 

“I thought for sure you realized it during last year. I thought you’d come to me when you were ready.”

“Last year?” 

Regenia forced herself to put her current predicament to the side. Last year Sirius was banished because…. Lupin. 

“Sirius’ soulmate.”

“His mark is the moon. Yours is the sun,” James whispered.

Regenia’s breath caught in her throat. How did James know that? Sirius had never seen it before. Which meant — there was no way James was her soulmate. Right? 

She hated him.

She hated his stupid laugh and his mischieveous hazel eyes. His dimple peeked out at the end of every smile. His wind-blown hair drove her crazy. His unwanted kindness and advice always came when she needed it most. Why did it have to be him?

“I’m stupid,” Regenia groaned. 

“But stupidly smart, too,” James rejoined, grin cracking his face. “I hear it runs in the family.”

Family. That’s what started everything in the first place. Regenia didn’t join in the humor. 

“Our bond is dying, Reggie. Why?” James asked after a few moments of silence. “Part of it has started to turn black.”

Regenia winced. Their bond was dying because of the promise Orion made to the Dark Lord on her behalf. As long as Orion was her Head of House in Magic, he could avow her body and magic as much as he pleased. 

The Black family had never cared about soulmates. Soulmates never meant more power or fortune.

“Orion promised me to the Dark Lord’s service. I’m to be presented at Yule.”

“No,” James spat. His magic visibly roiled at the news. Taking a deep breath, he strode forward and pulled her into his arms. “He’s not taking you, Reggie.”

“I don’t have a choice,” Regenia objected.

“Let me touch your mark.” 

James flushed red as soon as the words left his mouth, but his determination never left his eyes.

Regenia gaped at him. 

“What?” she squeaked.

“Our bond is dying. If we touch each other’s mark, it should overpower the fledgling bond you have with the Dark Lord.”

He was right. Damn him. 

If they poured their magic into the soulmarks at the same time, it would overwhelm the miniscule piece of magic the Dark Lord was feeding her. Their magical feedback would loop and seal their souls together. Regenia would be safe from any outside magical influences that wanted to tamper with her soul. 

James was her soulmate. He had been with her from the moment she was born. She could do this. 

Regenia pulled a few feet away and glanced into his eyes. “One word about my underwear and I will hex you into the hospital wing,” she threatened. 

She tugged down her skirt until the waistband rested below her soulmark. It almost looked like an eclipse in progress. The hint of red panties made her feel exposed.

“Well. What about you?” Regenia gestured toward his hip.

She blushed when he unbuttoned his pants and slid them down a few inches. The matching soulmark stole her breath. She never thought she would see her matching soulmark for the first time _like this_ while standing in a secret room on the seventh floor of Hogwarts a few weeks before Yule. 

She instinctively stepped forward and touched it. Her fingertips barely grazed his skin. She looked up at the sudden indrawn breath. She waited for a sarcastic comment or something to lighten the tension that filled the room.

“Dance with me,” James whispered against her cheek.

Regenia shuddered as their hands caressed each others soulmarks. The darkness that had pervaded the mark fought against the magic they imbued it with. They continued to pour more and more magic into the marks, chasing away the taint. When the loop of magic finally closed, she slumped against his chest. She could feel every shudder and beat of his heart.

She never wanted to leave his arms. 

**SEVENTH YEAR**

Regenia threw her graduation cap into the air with the rest of her year mates. She glanced around the Great Hall and smiled. So many memories had happened in this school. She made friends, joined the Slytherin Quidditch team, and won the House Cup three years in a row. She met an arrogant boy that stole her brother and who turned out to be her soulmate. She realized that her parents’ ideals were wrong and decided to join the Order of the Phoenix. 

She grew within these walls. She would dearly miss them.

“Hey, Reggie. Are you ready to leave? We’re going to miss the party!” James asked as he looped an arm around her waist.

Regenia rolled her eyes. James never stopped calling her Reggie. Her soulmate was stubborn and far too charming. She pulled him into a searing kiss and ignored his question entirely. She smiled as she pulled away. It always left him dazed for a moment. She loved being able to do that to him.

“We can’t be late to our own party, James. It’s not possible.”

“Well, maybe I don’t want to wait any longer,” James said. He kissed the side of her neck, drawing a giggle from her. “Sirius was in charg—”

“I thought we agreed it would be Remus,” Regenia said, with narrowed eyes. 

Sirius had no business being in charge of her engagement party. He would blow everything out of proportion. 

“Yes. Remus _was_ in charge. Then Sirius came up with ‘a super special awesome idea that would amaze everyone.’ His words, mind you, not mine. Remus can’t say no. You know that.”

Regenia sighed. Remus indulged Sirius far too much. She shook her head and leaned against James’ chest. 

His heart picked up speed. She smiled. 

“I used to hate you.”

“Hmmm.”

Regenia snorted and smacked his arm. “That’s all you have to say? Hmmm?”

“What do you want me to say? Uh, that sucked? I’m glad you chose me anyway?”

Regenia laughed loudly at his response. 

She didn’t hate James Potter. He was still far too charming and handsome, and he had the bad habit of calling her Reggie. 

But, she liked him despite his flaws.


End file.
